Microencapsulation

Dr. Pawar Anil R

Asso. Prof.

MESCOP, Sonai

Microencapsulation

Microencapsulation is a means of

applying thin uniform coatings to

microparticles of solids dispersion

or droplets of liquids.

Microcapsules are small particles that contain an active

agent (core material) surrounded by a shell or coating.

Their diameters generally range from a few microns to a

few millimetres.

Microcapsules can have many different types and

structures:

a) simple droplets of liquid core material surrounded by a

spherical shell (Microcapsules)

b) irregularly-shaped particles containing small particles of

solid core material dispersed in a continuous polymer shell

matrix )microspheres).

Microcapsules

Microencapsulated liquid

microspheres

Microencapsulated solid

Mechanisms for the release of encapsulated core materials:

Disruption of the coating by pressure, shear, or abrasion

forces.

Enzymatic degradation of the coating where permeability

changes.

Diffusion or leaching of core materials.

The rate of release of core material is a function of :

• the permeability of the coating to core material.

• the dissolution rate of the core materials

• the coating thickness

• the concentration gradient existing across the coating

membrane.

application of microencapsulation

Four important areas of microencapsulation application are :

1. The stabilization of core materials

2. The control of release or availability of core materials

3. Separation of chemically reactive ingredients within a

tablet or powder mixture.

4. Taste-masking.

1.The stabilization of core materials

Examples:

Microencapsulation of certain vitamins to retard

degradative losses.

Microcapsule stabilities of an anthelmintic (carbon

tetrachloride), methyl salicylate, and flavors.

Controlled release from microencapsulated products are

used for prolonged action or sustained-release

formulations

Example:

The application of varied amounts of an ethyl cellulose

coating to aspirin using coacervation phase-separation

encapsulation techniques, where release of aspirin is

accomplished by leaching or diffusion mechanism from the

inert, pH-insensitive ethvl cellulose coating.

2. The control of release or availability of core materials

Some Microencapsulated Core Materials

Final

Product

Form

Purpose of

Encapsulation

Characteristic

Property

Core Material

TabletTaste-maskingSlightly water-Acetaminophen

Soluble solid

Tablet or

capsule

Taste-masking;Slightly water-Aspirin

sustained release;Soluble solid

reduced gastric

irritation;

separation of incom

patibles

VariedSustained releaseSlightly water-

soluble solid

Progesterone

CapsuleReduced gastric irritationHighly water-

soluble solid

Potassium chloride

Microencapsules can be formulated as

powders and suspensions, single-

layer tablets, chewable tablets,

creams, ointments, aerosols,

dressings, plasters, suppositories, and

injectables.

Core Material

The core material is the material to be coated, which

may be liquid or solid in nature.

The composition of the core material can be varied:

The liquid core can include dispersed and/or dissolved

material.

The solid core can be a mixture of active constituents,

stabilizers, diluents, excipients , and release-rate

retardants or accelerators.

The coating material should:

• Be capable of forming a film that is cohesive with the core

material

• Be chemically compatible and non-reactive with the core

material

• Provide the desired coating properties, such as strength,

flexibility, impermeability, optical properties, and stability.

• Coating material selected from natural and synthetic film-

forming polymers like:

- carboxy methyl cellulose - ethyl cellulose

- cellulose acetate phthalate - poly vinyl alcohol

- gelatin, gelatin- gum arabic - poly hydroxy cellulose

- waxes - chitosan

Coating Materials

Microencapsulation methods

1. Air suspension

2. Coacervation-phase separation

3. Spray drying

4. Congealing

5. Pan coating

6. Solvent evaporation techniques

Microencapsulation Processes and Their Applicabilities

Approximate

Particle Size (µm)

Applicable Core

Material

Microencapsulation

Process

35-5000SolidsAir suspension

600-5000SolidsPan coating

1-5000Solids & liquidsMultiorifice

centrifugal

2-5000Solids & liquidsCoacervation-phase

separation

5-5000Solids & liquidsSolvent evaporation

600Solids & liquidsSpray drying and

congealing

A, control panel;

B, coating chamber;

C, particles being treated;

D, process airflow;

E, air distribution plate;

F, nozzle for applying film coatings.

Microencapsulation by air suspension techniques using

Wurster Air Suspension Apparatus

Air Suspension

Schematic drawings of Wurster Air Suspension Apparatus

Principle

1. The Wurster process consists of

the dispersing of solid particulate

core materials in a supporting air

stream and the spray-coating of

the air suspended particles.

2. Within the coating chamber,

particles are suspended on an

upward moving air stream as

indicated in the drawing.

3. The design of the chamber and its

operating parameters provide a

recirculating flow of the particles

through the coating zone portion

of the chamber, where a coating

material, usually a polymer

solution, is spray-applied to the

moving particles.

4. During each pass through the

coating zone, the core material

receives an increment of coating

material.

5. The cyclic process is repeated several times during

processing, depending on the purpose of microencapsulation,

the coating thickness desired.

6. The air stream also serves to dry the product while it is being

encapsulated.

The process has the capability of applying coatings in the

form of solvent solutions, aqueous solutions, emulsions,

dispersions, or hot melts

The coating material selection appears to be limited only

in that the coating must form a cohesive bond with the

core material.

The process generally is applicable only to the

encapsulation of solid core materials

Particle size, The air suspension technique is applicable

to both microencapsulation and macroencapsulation

coating processes with particle size range 35-5000 µm

Coacervation-Phase Separation

Step 1. formation of three immiscible

chemical phases (vehicle ,Core and

liquid coating).

Coating formation during coacervation phase-separation process

consists of three steps carried out under continuous agitation:

Step 2. Deposition of liquid

coating material.

Step 3. Rigidization of the coating

Step 1 Formation of three immiscible chemical phases:

A liquid manufacturing vehicle phase, a core material phase,

and a coating material phase.

To form the three phases, the core material is dispersed

in a solution of the coating polymer, the solvent for the

polymer being the liquid manufacturing vehicle phase.

The coating material phase, an immiscible polymer in a

liquid state, is formed by utilizing one of the methods of

phase separationcoacervation:

by changing the temperature of the coating polymer

solution

by adding a salt, nonsolvent, or incompatible polymer to

the polymer solution; pH change;

by inducing a polymer-polymer interaction.

Step 2Depositing the liquid polymer coating upon the core material.

This is accomplished by controlled, physical mixing of the

coating material (while liquid) and the core material in

the manufacturing vehicle.

Deposition of the liquid polymer coating around the core

material occurs if the polymer is adsorbed at the

interface formed between the core material and the

liquid vehicle phase, and this adsorption phenomenon is

a prerequisite of coating.

The continued deposition of the coating material is

promoted by a reduction in the total free interfacial

energy of the system, by the decrease of the coating

material surface area during coalescence of the liquid

polymer droplets.

Step 3

Rigidizing the coating,

By thermal , cross-linking (formaldehyde), or desolvation

techniques, to form a self-sustaining ذاتيامكتفية

microcapsule.

Temperature Change Point X represent a system exists as a single-phase,

homogeneous solution.

As the temperature of the system is decreased (B) , Phase

separation of the dissolved polymer occurs in the form of

immiscible liquid droplets, and if a core material is present

in the system, under proper polymer concentration,

temperature, and agitation conditions, the liquid polymer

droplets coalesce around the dispersed core material

particles, thus forming the embryonic microcapsules.

The phase-boundary curve indicates that with decreasing

temperature, one phase becomes polymer-poor (the

microencapsulation vehicle phase) and the second phase

(the coating material phase) becomes polymer rich

The loss of solvent by the polymer-rich phase can lead to

gelation of polymer, and hence rigidization or solidification

of the microcapsule polymeric coating.

Temperature-composition phase diagram for a binary system of a

polymer and a solvent.

TE

MP

ER

AT

UR

E

POLYMER CONCENTRATION %

X

A

BC D

E

F G

Incompatible Polymer Addition

• The diagram illustrates a

ternary system consisting of a

solvent, and two polymers, X and

Y.

• If an immiscible core material

Polymer X is dispersed in a

solution of polymer Y (point A) ,

the phase boundary will be

crossed at point E.

A

BC D

E

SOLVENT

100%

100%

POLYMER Y

100%

POLYMER x

Phase diagram for phase-separation/ coacervation induced by Incompatible

Polymer Addition

As the two-phase region is penetrated with the further

addition of polymer X, liquid polymer, immiscible droplets

form and coalesce to form microcapsules.

The polymer that is more strongly adsorbed at the core

material-solvent interface, (in this case polymer Y),

becomes the coating material.

Solidification of the coating material is accomplished by

further penetration into the two-phase region, washing the

embryonic microcapsules with a liquid that is a nonsolvent

for the coating, polymer Y, and that is a solvent for polymer

X.

Nonsolvent Addition

A liquid that is a non-solvent for

a given polymer can be added to

a solution of the polymer to

induce phase separation, as

indicated by the general phase

diagram.

The resulting immiscible, liquid

polymer can be utilized to

microencapsulation of an

immiscible core material.

A

B

C

DE

SOLVENT

100%

100%

POLYMER

100%

NON SOLVENT

Phase diagram for phase-separation/ coacervation induced by Non Solvent

Addition

Salt Addition

Soluble inorganic salts can be

added to aqueous solutions of

watersoluble polymers to cause

phase separation. As sodium

sulfate.

A

BC

DE

WATER

100%

100%

POLYMER

100%

SALTS

Phase diagram for phase-separation/ coacervation induced by Salt Addition

Polymer-Polymer Interaction (Complex Coacervation)

The interaction of oppositely charged

polyelectrolytes can result in the

formation of a complex having

reduced solubility and phase

separation occurs.

Complex coacervation process consists of

three steps:

1. Formation of an O/W emulsion

2. Formation of the coating

3. Stabilization of the coating

The phase diagram for a ternary system

comprised of two dissimilarly charged

polyelectrolytes in water (as solvent).

A

C

B

WATER

100%

100%

P -100%

P+

Phase diagram for phase-separation/ coacervation

induced by Polymer Interaction

X

In the dilute solution region, interaction of the oppositely

charged polyelectrolytes occurs, inducing phase separation

within the phaseboundary curve ABA.

The segmented tie-lines indicate that a system, having

an overall composition within the two-phase region (point C

for example), consists of two phases, one being polymer

poor, point A, and one containing the hydrated, liquid

complex, Pe+ and Pe-, point B.

Gelatin and gum arabic are typical polyelectrolytes that

can interact.

Gelatin, at pH below its isoelectric point, possesses a

positive charge, whereas the acidic gum arabic is negatively

charged.

Under the proper temperature, pH, and concentrations,

the two polymers can interact through their opposite

electrical charges, forming a complex that exhibits phase-

separation/coacervation.

Typical drying methods such as spray, freeze, fluid bed

and tray drying techniques can be used in the

microencapsulated products.

Microcapsules can be manufactured by phase-

separation/coacervation processes in large scale in vessels

up to 2000 gallons in capacity.

Solvent evaporation

This method of microencapsulation is the most widely used due to:

1. Simple technique .

2. this method allow encapsulation of hydrophobic and hydrophilic

drug

3. this method allow encapsulation of solid and liquide drug

4. Microcapsule produced have wide size rang (5-5000µm)

Pan Coating

applied in the coating pans to remove the coating solvent.

• Final solvent removal is accomplished in a drying oven.

• The coating operation is repeated three times. Then coating

followed by dusting with talc the microcapsules are rolled until

drying, and the excess talc is removed by vacuum.

The product is then screened through a 12mesh screen.

Pan Coating process is used for

solid particles greater than 600

microns in size.

The coating is applied as a solution,

or as an atomized spray, to the

desired solid core material in the

coating pan.

Warm air is passed over the coated

materials as the coatings are being

Spray Drying and Spray Congealing

The Spray dryer equipment

components include :

•An air heater

•Atomizer spray chamber

• Fan

• Cyclone

•Product collector.

Microencapsulation is conducted by

dispersing a core material in a

coating solution, in which the coating

substance is dissolved and in which

the core material is insoluble, and

then by atomizing the mixture into a

heated air stream.

Microencapsulation by spray-congealing can be

accomplished with spray drying equipment when the coating

is applied as a melt .

General process variables and conditions are quite similar

to those spray drying , except that the core material is

dispersed in a coating material melt rather than a coating

solution.

Waxes, fatty acids polymers , alcohols, and sugars, which

are solids at room temperature but meltable at reasonable

temperatures, are applicable to spray-congealing techniques.

Coating solidification (microencapsulation) is accomplished

by spraying the hot mixture into a cool air stream.

Microcapsules add many functional benefits

• particularly in skin care and treatment products include :

Acting as controlled release vehicles

Offering stabilization of materials that would otherwise

be unstable.

Act as delivery enhancers for active ingredients.

Complex coacervation allows core contents to be varied

to include almost any combination of oils, waxes, fats,

butters, flavors, lipophilic actives, fragrances and other

beneficial additives .